1. Field of the Invention
The present invention relates to a polyimide compound, a preparation method therefor, and an optical film and an optical waveguide produced by employing the compound.
2. Description of the Related Art
Conventionally, plastic materials containing essentially a polyimide resin, an epoxy resin or an acrylate resin are often used in the field of optics. Such optical resins are generally required to have heat resistance, moisture resistance and other various properties depending upon their applications. To this end, various types of optical resins have been developed, which are imparted with various properties by modifying a main chain and a side chain of a polymeric skeletal structure. Particularly, highly transparent plastic materials for use as sealing materials for optical elements and for use as materials for flexible wiring boards are now under consideration for application to optical waveguides (see JP-A-2003-89779, JP-A-HEI8 (1996)-41323 and JP-A-2002-201231).
With the recent trend toward higher information capacity and higher information transmission speed, focus is directed to development of opto-electric hybrid boards. Such a board typically includes a metal substrate (including a substrate having a metal layer) and an optical waveguide provided on the substrate. Depending upon the type of the substrate to be used, the linear expansion coefficient of a resin material for the optical waveguide should be properly controlled. This is because the metal substrate has a low linear expansion coefficient while a conventional ordinary resin material for the optical waveguide has a higher linear expansion coefficient. Where a layer of the resin material is formed on the metal substrate, the resulting board is liable to be thermally warped (or curled) (due to heat applied during production thereof or ambient heat applied after the production thereof).
A conceivable approach to this problem is to introduce a crosslink structure into the resin material to reduce the linear expansion coefficient. The easiest method for providing the crosslink structure is, for example, to introduce a multifunctional group. However, this method suffers from gelation of a polymer, making it difficult to form a coating film by applying a resin composition (e.g., by a spin coating method or the like) for the formation of the optical waveguide or the like.
In view of the foregoing, it is an object of the present invention to provide a novel polyimide compound which has a low linear expansion coefficient and permits film formation by the spin coating method or the like, a preparation method for the compound, and an optical film and an optical waveguide produced by employing the compound.